Extract desirable column from .txt file... how....

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Extract desirable column from .txt file... how....

Dear my fellas..

I have a text file, containing student's number, students name, respectively..

Example:

343;john;doe
544;jessy;dolphin
113;michael;iron
.
.

My aim is, I want to extract 2nd column and send it to the combobox.

In example, I want to extract values 'john,jessy,michael,...' from .txt file .

How could I accomplish that?

Any idea, any example will be so helpful....

I am waiting.

August 23rd, 2012, 09:25 AM

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You can accomplish this using the COPY function which returns a substring of a string and use POS and POSEX functions to define the start and end of your sub-string.

Code:

function ExtractName(InStr: String): String;
var
   StartPos: Integer;
   StrLength: Integer;
begin
   StartPos := Pos(';',InStr)+1; 
   //Start just after ';'
   StrLength := PosEx(';', InStr, StartPos) - StartPos;
   //get pos of 2nd ';' subtract startpos to get length
   result := Copy(InStr, StartPos, StrLength);
   //Add StrUtils to your uses clause for PosEx function.
end;

Usage:

Code:

S := '343;john;doe';
ComboBox1.Items.Add(ExtractName(S));

//you'll need to do this in a loop assigning each string in turn.

August 26th, 2012, 04:14 PM

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Changing a little bit it, I changed it to the format:

var
startpos:integer;
strlength:integer;
procedure ExtractName(InStr: String): String;
begin

startpos:=pos(';',Instr)+1;
strlength:=posex(';',instr,startpos)-startpos;
result:=copy(instr,startpos,strlength);

end;

then it gave me errors:

undeclared identifier: Instr
undeclared identifier: posex
undeclared identifier: result

I am not sure which data type they will have.

please help....

Quote:

Originally Posted by majlumbo

You can accomplish this using the COPY function which returns a substring of a string and use POS and POSEX functions to define the start and end of your sub-string.

Code:

function ExtractName(InStr: String): String;
var
   StartPos: Integer;
   StrLength: Integer;
begin
   StartPos := Pos(';',InStr)+1; 
   //Start just after ';'
   StrLength := PosEx(';', InStr, StartPos) - StartPos;
   //get pos of 2nd ';' subtract startpos to get length
   result := Copy(InStr, StartPos, StrLength);
   //Add StrUtils to your uses clause for PosEx function.
end;

Usage:

Code:

S := '343;john;doe';
ComboBox1.Items.Add(ExtractName(S));

//you'll need to do this in a loop assigning each string in turn.

August 26th, 2012, 05:49 PM

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Why change what is correct?
1.
You changed from a function to a procedure therefore
undeclared identifier: result

2.
You moved
StartPos and StrLength variables outside the procedure.
Wrong approach
You should not declare local variables as global.
All variables should be declared with the least scope possible
to accomplish their task.

3.
undeclared identifier: posex
Did you include StrUtils in your uses clause as instructed?

4.
undeclared identifier: Instr
No idea. From what you actually posted, I can see no reason for that.
Is this an exact representation of your real code?
Alternatively, it might be related to your changing from function
to procedure without removing the return parameter from the declaration.

Clive

Last edited by clivew : August 26th, 2012 at 05:54 PM. Reason: Added comment about declaration to item 4.

August 27th, 2012, 01:32 PM

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Including strutils header to the program, and using function, works perfectly!..

Thank you.

August 27th, 2012, 01:46 PM

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Quote:

Originally Posted by turkalpk

Including strutils header to the program, and using function, works perfectly!..

Thank you.

One last question. How could I retrieve 1st column ? and 3rd column?

Using the same functions (Copy, Pos and PosEx)

To get the 1st and 3rd columns

Code:

function FirstColumn(InStr: String): String;
begin
   Result := copy(InStr, 1, pos(';', InStr)-1);
   //return the string between the 1st character and 
   //just before the first ';'
end;

function ThirdColumn(InStr: String): String;

   function PosN(LookFor, LookIn: String; nthPosition: Cardinal): Integer;
   //This function will find the Nth occurrence of LookFor
   //in LookIn.  
   //If it returns 0, then that Nth occurrence does not exist.
   //You want to find the 2nd ';' in the string..
   //notice that it is embedded within the ThirdColumn function
   //It can stand as a separate function, but if the functionality
   //isn't required elsewhere, keep it within ThirdColumn
   var
      I, CurPos: Integer;
   begin
      CurPos := 0;
      For I := 1 to nthPosition do
      begin
         CursPos := PosEx(LookFor, LookIn, CurPos+1);
         if CurPos := 0 then
            Break;
      end;
      Result := CurPos;
   end;

begin
   Result := Copy(InStr, PosN(';', InStr, 2)+1);
   //return the string after the 2nd ';'
end;

August 28th, 2012, 09:34 AM

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thank you so much.
working perfectly.

September 4th, 2012, 03:36 PM

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I could not be able to run function to get third column.

I could not be able to run function to get third column.

var i,curpos:integer;
function thirdcolumn(instr:string):string;
begin
function posn(LookFor,lookin:string;nthposition:cardinal):integer; begin
curpos:=0;
for i := 1 to nthposition do begin curpos:=posex(lookfor,lookin,curpos+1);
if curpos:=0 then break;
end;
result:=curpos;
end;
result:=copy(instr,posn(';',instr,2)+1);
end;
end.

Please help. I am waiting.

September 4th, 2012, 04:50 PM

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Quote:

result:=copy(instr,posn(';',instr,2)+1);

Code:

result:=copy(instr,posn(';',instr,2)+1,maxint);

You forgot the last parameter for copy.
Using maxint, of course, assumes that the third column is the final column.

#10

September 4th, 2012, 05:46 PM

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Quote:

Originally Posted by clivew

Code:

result:=copy(instr,posn(';',instr,2)+1,maxint);

You forgot the last parameter for copy.
Using maxint, of course, assumes that the third column is the final column.

If the final value is not provided in the copy command, then copy defaults to the rest of the string, so there's no difference, between, no value and maxint.
So

Code:

result:=copy(instr,posn(';',instr,2)+1);

is functionally equivalent to

Code:

result:=copy(instr,posn(';',instr,2)+1,maxint);

#11

September 4th, 2012, 05:55 PM

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Can you debug and see what value is being returned by PosN? Compare it to your input string and make sure it is returning the correct position.

#12

September 4th, 2012, 08:49 PM

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Here is the error I get form posn.

#13

September 4th, 2012, 09:14 PM

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OK. Its much easier to help (I hope!) with the error messages,
as I have posted in this forum so many times.

The inner function needs defining before the begin of the outer function not after.

Clive

#14

September 4th, 2012, 11:04 PM

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As Clive mentioned you have moved the begin statement to the incorrect place.

Here is how the function(s) should look:

Code:


function ThirdColumn(InStr: String): String;



   function PosN(LookFor, LookIn: String; nthPosition: Cardinal): Integer;
   var
      I, CurPos: Integer;
   begin
      CurPos := 0;
      For I := 1 to nthPosition do
      begin
         CursPos := PosEx(LookFor, LookIn, CurPos+1);
         if CurPos := 0 then
            Break;
      end;
      Result := CurPos;
   end;


begin
   Result := Copy(InStr, PosN(';', InStr, 2)+1);
end;

#15

September 5th, 2012, 12:41 AM